Underbetting by mersenneary   As people were learning HUSNGs, a general consensus arose that bets should tend to be between half the size of the pot and the full size of the pot. However, there's nothing mathematically magical about that half pot number. In fact, there are plenty of situations where betting smaller is optimal. Typically, when I underbet, it's because my range is stronger than yours, but it also has plenty of weaker hands in it. Your range contains plenty of air, and what I'm saying is, “so what are you going to do about it?” This is widely applicable throughout poker. In MTTs, we make small 3bets in position because it represents a strong range, our opponent has plenty of weaker hands that still have to fold despite the size, and it doesn't matter that we too can be fairly light. “What are you going to do about it?” is exactly what we're asking. That's also why open raise sizes in MTTs went from being 3x or even 3.5x down to 2-2.2x as the game evolved. I'm opening the pot. I have a stronger range than you do. What are you going to do about it? The smaller size allows you to contest more pots and risk less while doing it. Naturally, I wouldn't be talking about it if it weren't very applicable to HUSNGs. Let's look at examples.   Hand 1: We raise the button and get called. Flop is A72 with two spades and we continuation bet 1/3 of the pot. Hand 2: Minraise the button with A2 and get called. Flop is Q55. We c-bet 1/3 of the pot. Hand 3: We 3bet from the big blind, and the flop comes K52 rainbow. There is now 400 in the pot with 700 effective stacks behind. We continuation bet t150, or 37.5% of the pot. Hand 4: Minraise the button 32bb deep. The flop comes A95 rainbow. Our opponent, who we know is capable of doing this with a wide range including middle and button pair, leads out for half the pot. We make a small raise to t90, and get called. The turn is a 2, and with t260 in the pot and t490 behind, we bet t95. When called, we jam t395 into t450 on the river. Hand 5: Minraise the button. Flop comes Q62 with two spades. We continuation bet, and our opponent check/raises. We either make a small 3bet back, or call and underbet the turn.   Starting with Hand 1. Here, it's often good to underbet as a continuation bet because we have a stronger range and are in a stronger position than our opponent does. Our opponent's range contains a lot of air, and people tend to be fairly fit or fold on this flop. Thus, underbetting gives us a cheaper price to win the hand which adds up over time. It's also worth noting that we're not done with the hand when called. Most opponents who just call a small flop bet here have a rather weak range, even after they indicate that they do not have a hand in their substantial air range. Betting flop this way is a good method of getting information about your opponent's holdings even when called, and because you represent an inducing hand well on the flop you can follow through with some very profitable bluffs. In the second hand, we have a specific holding where there's really no need to make a full-sized continuation bet against the vast majority of opponents. We want to continuation bet here to not give our opponent free cards to realize his 25% equity (with JTo in the big blind, you're hoping you don't have to face a c-bet). We'll also get some thin value from king high and floats. There's no need to bet a full half pot to accomplish these things, especially the folding out equity we'll never get value from, which is the case the majority of the time here. So bet 1/3 of the pot and ask your opponent what he's going to do about it. Most of the time, the answer is nothing. In the third hand, we'll have 3bet bluffs in our range but also clearly the stronger set of holdings. There's no need to ever bet half pot here on the flop. There's no threat of losing out on money with our value hands, our opponent pretty much has to just decide whether to get it in or not. A size even as low as t90 may actually be best on this flop – there's just so much air in the button's range and no issues with losing out on value with a smaller bet. In the fourth hand, we don't need to bet big on the turn to eventually get the fold equity we're looking for. The small flop raise and turn bet represents value hands super well, and makes for a very credible river jam. I usually take this line exclusively for value against non-thinking players, far more weighted to bluffs against thinking-but-nitty villains, and with a balanced range against the best opponents. Underbets can be used to serve whatever purpose you're trying to accomplish against your specific opponent. In the last hand, our opponent represents a strong range by check/raising, but most good players will have plenty of air in it. We can represent an even stronger range, and the best way to do that is to click it back. We can also choose to represent a range of more moderate strength by calling, and then follow up on that with a small turn bet when checked to – very often optimal with hands that would call the check/raise, and a very profitable bluff line against opponents who like to check/raise the flop light but give up when caught. In all these examples, a smaller betting amount is actually better than a big one in putting our opponent to the test with our entire range. There are some common themes in these examples other than what I mentioned at the start of the article. The flops I'm using tend to be dry – the more often your opponent has a weak pair or gutshot, the more you can play into what your opponent wants by making the price to continue cheap, especially if you don't follow up on future streets. The stack sizes tend to be shorter – we do want to get full value from our value range, and that's why underbetting is more effective with our entire range at shorter stacks. In heads-up cash, good players don't c-bet less than half pot on a dry board (and usually 2/3) against other decent players for a few other reasons (people call less wide from the BB, for example), but also because you need to be able to leverage your stack in position. That becomes less of a factor the shorter we get. Underbetting is a great way both to be exploitative when appropriate and to stay balanced if you need to. Probably the biggest benefit is that players tend to be terrible at adjusting to it when used in the right situations. It can induce and lead to a lot of spew, and can also just print money against uncreative opponents who are too hesitant to get out of the box. Keep thinking about how to use it appropriately.